The objective of this work is to evaluate an alternate form of tonography for the differential diagnosis of glaucoma. This tonographic method known as Constant Pressure Tonography has been shown to work in principle, but it is not used routinely in clinical practice because a practical instrument is lacking for this form if tonography. We have developed such an instrument and have a program underway for its evaluation. The accuracy made possible with such an instrument can lead to a significant improvement in the diagnostic value of the aqueous facility measurement. The standard tonography procedure now in use for this measurement is believed to have errors that range from 50% to 100%. Our analysis and laboratory tests indicate that, by using the constant pressure tonography procedure, a 10 to 20% precision for measuring facility can be attained. Our work consists of: (1) laboratory testing and validation of instrument, (2) clinical evaluation using selected patients, (3) further development of the instrument to achieve reliable performance in the clinical environment.